A high mechanical strength is required for a ball-and-roller bearing used under conditions of a high temperature and a high rotating speed like the ball-and-roller bearing used in an engine of an aircraft. Particularly, since only a slight damage done to a member is likely to bring about a serious accident in an aircraft, a very high mechanical strength and reliability is required for the ball-and-roller bearing for an aircraft.
For the same reasons, the ball-and-roller bearing for an aircraft is judged in general to have reached the life at the time when only a slight rust has been formed. Such being the situation, the ball-and-roller bearing for an aircraft is required to exhibit not only a high mechanical strength but also an excellent corrosion resistance.
It was customary to use a semihice series materials of AISI M50, M50NiL, etc. for forming the ball-and-roller bearing for an aircraft. The ball-and-roller bearing for an aircraft that is made of these materials exhibits a relatively high mechanical strength. However, in these materials, a content of chromium that is said to be most effective for improving the corrosion resistance of the steel is low.
In general, an airport is constructed near the coast, since the airport requires a tremendously large site and serious noises are generated by the aircraft around the airport. What should be noted is that the ball-and-roller bearing for an aircraft is used or stored under the environment in which rust tends to be caused by salt.
In the ball-and-roller bearing for an aircraft that is made of the semihice series material, the problem derived from the rust is not so serious in respect of the rolling body. This is because the rolling body has a small surface area, compared with other members. In addition, the most portion of the surface is brought into a rolling or sliding contact with other members. However, each of the inner ring and the outer ring has a large surface area, and the most portion of the surface is not brought into a rolling or sliding contact with other members. In addition, the ball-and-roller bearing for an aircraft including an inner ring or an outer ring made of the material described above fails to exhibit a sufficiently high corrosion resistance.
A martensite series stainless steel such as SUS440C is known to be suitable for use as a material of the ball-and-roller bearing excellent in corrosion resistance. However, in the case of using a martensite series stainless steel for forming the ball-and-roller bearing for an aircraft, coarse eutectic carbide particles are formed in the inner ring, outer ring, etc. As a result, it is not possible to obtain a hardness high enough to be used satisfactorily under the particularly severe conditions of a high temperature and a high rotating speed. Under the circumstances, it is important to improve further the rolling fatigue life characteristics of the ball-and-roller bearing.